Calcium chloride and alkali metal salts such as sodium chloride are used extensively in large quantities on roads for snow and ice removal. The problem with using salt as a deicing composition is that salt is liable to clump or cake during periods of extremely low temperatures or during temperature and humidity fluctuations. The caking causes difficulties in dispensing the salt evenly on the roads.
In order to avoid caking or hardening, preservatives or anticaking agents have been added to the deicing compositions. The water soluble ferrocyanide salts, such as sodium and potassium ferrocyanide, Na.sub.4 Fe(CN).sub.6.x H.sub.2 O (also commonly called yellow prussiate of soda or "YPS") and K.sub.4 Fe(CN).sub.6.x H.sub.2 O, where x=0 to 10, are common and highly effective anticaking agents. Water soluble ferricyanide salts can also be used as effective anticaking agents. Sodium ferricyanide has the formula: Na.sub.3 Fe(CN).sub.6.y H.sub.2 O and potassium ferricyanide has the formula: K.sub.3 Fe(CN).sub.6.y H.sub.2 O wherein y=0 or 1. Even though these alkali metal ferrocyanides and ferricyanides work very well as anticaking agents in deicing photodecomposition of the ferrocyanide to cyanide in the deicing composition.
The photodecomposition of the deicing compositions containing a cyanide such as a ferrocyanide composition is of particular concern, especially among road crews in the Northeastern United States. See "Rock Salt Cyanide Stirs Road Crew Health Concerns" The Journal of Commerce Dec. 28, 1989. The problem is that the deicing composition is typically stored in bulk (large piles) outdoors. When the composition is exposed to sunlight and moisture, it may decompose, thereby releasing cyanide, which can be highly toxic. There is concern among the transportation workers who handle deicing compositions because they may have a harmful atmosphere around them by virtue of cyanide being released from the anticaking component of the composition.
Thus, it is highly desirable to have a deicing composition that possesses anticaking properties, or is spreadable, yet does not photodecompose or release cyanide into the environment when exposed to sunlight.